<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <style type="text/css">
        /* 画三角形 */
        
        #mydiv {
            height: 0px;
            width: 0px;
            border-left: 100px solid transparent;
            border-right: 100px solid transparent;
            border-bottom: 100px solid red;
        }
    </style>

    <body>
        <div id="mydiv"></div>
    </body>
    <script>
        var ob = {
            name: "wswj",
            age: 12
        };
        ob.name = "ws";
        console.log(ob.age);
        // typeof number string boolean object undefined function
        //typeof(null)为object
        //undefinde null 没有tostring方法
    </script>
</body>

</html>